Color corrected high resolution imaging

ABSTRACT

A high resolution imaging system includes an imaging camera array creating a sets or frames of array images of a scene and a reference camera creating reference images of the same scene. A synchronization controller coordinates imaging of the scene by the imaging camera array and the reference camera. An image processor merges the sets of array images into high resolution images and apply a color correction to the high resolution images based on reference images. Color correction can be performed on the merged high resolution image or on individual array images prior to merger into the high resolution image

BACKGROUND

Arrays of video and still imaging cameras have been created to generateimages of scenes in very high resolution. Camera arrays generate aplurality of images which are then merged to create a high resolutionimage. Color correction techniques have been applied to the highresolution images based on automatic color matching between therespective images from the array. The accuracy of these color correctiontechniques under these conditions is limited in the ability to presentan accurate color representation of the scene being imaged.

SUMMARY

The technology includes an imaging apparatus having camera array, areference camera, a camera synchronization controller and an imageprocessor. The camera array comprises a plurality of imaging cameras,each having a camera field of view, each camera field of view offsetwith respect to at least one adjacent imaging camera field of view, thecamera field of views combined to provide an array field of view. Thereference camera has a field of view at least partially overlapping thearray field of view. The synchronization controller is coupled to thecamera array and the reference camera, and directs imaging of a scene inthe reference camera field of view and the array field of view. Thereference camera provides at least one reference image of the referencecamera field of view. The image processor creates a high resolutionimage from the array images and applies a color correction based on atleast one reference image to the high resolution image formed from theplurality of array images either before or after creating of the highresolution image.

In another aspect, a method of creating a color corrected highresolution image is provided. The method includes obtaining a set of aplurality of at least partially overlapping commonly exposed images of afield of view of a first scene. The method further includes obtaining areference image of a second field of view including the scene. Thereference image has a greater color depth than each of the plurality ofat least partially overlapping commonly exposed images. A colorcorrection is applied to the plurality of at least partially overlappingimages based on the color depth of the reference image to create acolor-corrected high resolution image.

In a further aspect, a high resolution imaging device includes a firstcamera system, a second, reference camera system and an image processor.The first camera system is adapted to generate video imaging comprisinga plurality of frames. Each frame comprises a set of plurality ofcommonly exposed images of a scene. Each of the plurality of commonlyexposed images includes at least a portion of a field of view of thescene and at least partially overlaps at least one adjacent image havinga different portion of the field of view. The second camera system isadapted to generate a plurality of reference images of the scene from areference field of view. Each of the plurality of reference images has acolor depth greater than a color depth of each of the plurality ofcommonly exposed images, at least a portion of the plurality ofreference images commonly exposed with ones of the plurality of frames.The image processor includes a color corrector to apply a colorcorrection based on at least one of the plurality of reference images toa corresponding one of the plurality of frames, and an image stitcher tocreate a high resolution image from the color corrected plurality ofimages.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a first embodiment of a high resolution imaging apparatuswith color correction.

FIG. 2 is a block diagram illustrating a first exemplary use of the highresolution imaging apparatus.

FIG. 3 is a flowchart of a process performed by the high resolutionimaging apparatus to create high resolution imaging from a camera arraywith color correction based on a reference image.

FIG. 4 is a flowchart of a first embodiment of a method performed by animage processor to apply color correction based on a reference image toimages generated by imaging apparatus.

FIG. 5 is a flow diagram illustrating a first embodiment of determininga color correction between a reference image and a high resolution imageformed from a plurality of images created by a camera array.

FIG. 6 is a flow diagram illustrating another embodiment of determininga color correction between a reference image and a high resolution imageformed from a plurality of images generated by a camera array.

FIG. 7 is a flowchart of a second embodiment of a method performed by animage processor to provide high resolution imaging with color correctionbased on a reference image.

FIG. 8 is a flow diagram illustrating a first embodiment of determininga color correction between a reference image and one of a plurality ofarray images prior to creation of a high resolution image.

FIG. 9 is a flow diagram illustrating another embodiment of determininga color correction between a reference image and one of a plurality ofarray images prior to creation of a high resolution image.

FIG. 10 is a flow diagram illustrating a method performed to performedge region color correction in ones of a plurality of images used tocreate a high resolution image.

DETAILED DESCRIPTION

Technology is presented to enhance the color of high resolution videoand still imaging. The technology includes an apparatus having animaging camera array creating a plurality of array images of a scene anda reference camera creating a reference image of the same scene. Asynchronization controller coordinates imaging of the scene by theimaging camera array and the reference camera. An image processor isutilized to merge the array images into a high resolution image andapply a color profile from a reference image to the high resolutionimage. Color correction can be performed on the merged high resolutionimage or on individual array images prior to merger into the highresolution image.

Imaging camera arrays have been utilized to provide high resolutionarray images which are created by stitching together the array imagescreated by the array. The result is a high-resolution still image orvideo frame which can be utilized in the numerous products. Cameraresolution is one of the factors which affects the perceptual quality ofpictures and videos. Another factor is the color quality of the picture.Normally, after image stitching, the overall contrasting color of thepicture will be degraded. Previous embodiments of imaging camera arraysuse color enhancement algorithms in an attempt to optimize the color thepicture so that it looks more visually pleasing to the human eye.However, these color correction algorithms do not recover the true colorof the captured scene. In addition, color information has been partiallylost during the imaging process, the improvement by color enhancementlimited due to lack of information.

The present technology applies color correction based on the referencecamera's high color quality image of a scene which is commonly exposedby the imaging camera array. The output of the imaging camera array is aset of array images of the scene which are merged or stitched to createa high resolution image. Various techniques of color correction may beused as described herein.

As used herein, commonly exposed images are images that are created inrelatively close temporal proximity. As such, a set of array images maybe commonly exposed with each other if they are simultaneously exposed(all array cameras imaging in parallel) or in temporal proximity suchthat their merging creates a relatively uniform high resolution imagebased on their exposure of a scene. Commonly exposed images may besimultaneously exposed, but simultaneous exposure is not required.Reference images may be commonly exposed with array images where thetemporal separation between the reference and array images would notfrustrate applying the color profile of the reference image of a scenefrom the reference image to a high resolution image created from the setof array images. In view of the foregoing, temporal separation forcommonly exposed array images within a set of array images for a sceneshould be small, on the order of fractions of a second, in order topreserve details of the scene. Temporal separation for commonly exposedimages between a reference image and a set of array images may belonger, on the order of seconds, but may also be fractions of a secondor exposed simultaneously.

FIG. 1 illustrates a first embodiment of an apparatus 100 in accordancewith the present technology. Imaging apparatus 100 includes an imagingcamera array 155, a reference camera 195, a synchronization (sync)controller 175 coupled to both the imaging camera array 155 and thereference camera 195 and an image processor 102 also operationallycoupled to array 155 and camera 194. Connection between thesynchronization controller 175, processor 102 camera 195 and array 155may be by a direct wired connection, direct wireless connection orwired/wireless network connection. The sync controller 175 may be astandalone controller operable to control the exposure of the imagingcamera array 155 and the reference camera 195 to ensure common exposurebetween reference camera and the imaging camera array 155 when bothdirected at a scene (as in FIG. 2 herein). Imaging camera array 155 maybe comprised of a plurality of individual imaging camera array cameras,four of which array cameras 155 a, 155 b, 155 c and 155 d are noted inFIG. 1. In one embodiment, each of the array cameras illustrated inimaging camera array 155 is of identical construction such that thelenses, controller, image sensor and any camera controller attachedthereto may be identical.

Any number and arrangement of array cameras 155 a, 155 b, 155 c, 155 d .. . 155 n (where “n” is any whole number) may be utilized in the imagingcamera array 155. Each array camera 155 a, 155 b, 155 c, 155 d . . . 155n has a field of view which partially overlaps an adjacent cameras fieldof view. For example, camera 155 a has a field of view overlapped bycameras 155 b, 155 c and 155 d. In some embodiments, no overlap betweenadjacent cameras is used; in other embodiments, the amount of overlapbetween adjacent cameras—for example array cameras 155 b and 155 c—is upto 50% of each camera's field of view. Each array camera in such examplemay have from one to eight overlapping array camera fields of view. Forexample, array camera 155 a may have three overlapping fields of viewwhile camera 155 c may have eight overlapping fields of view. As aresult, each array image created by an array camera will partiallyoverlap an adjacent array image on one or more sides. Those cameras inthe imaging camera array 155 positioned so as to be surrounded by eightcameras will have potentially eight overlapping regions. It should beunderstood that the amount of overlap between the adjacent cameras inthe array may be determined in accordance with the particularconfiguration of the imaging camera array 155.

Each array camera 155 a, 155 b, 155 c, 155 d . . . 155 n may beindependently controlled and coupled to an independent control processorcoupled to the sync controller and/or the image processor 102. Eacharray camera 155 a, 155 b, 155 c, 155 d . . . 155 n may have aresolution from one to many mega-pixels. Each array camera 155 a, 155 b,155 c, 155 d . . . 155 n may comprise a still image camera or a videocamera operable to provide video at a frame rate of 24-300 frames persecond (fps). In the context of this disclosure, discussion ofprocessing of an “image” is equivalent to processing a “frame” of imagedata from a video stream.

Examples of imaging camera arrays suitable for use in accordance thepresent technology are described in 2005. High performance imaging usinglarge camera arrays. ACM TOG 24, 3, 765-776 and the AWARE2 MultiscaleGigapixel Camera (http://www.disp.duke.edu/projects/AWARE/index.ptml).In the context of this technology, the imaging camera array can be anytype of image capture system which provides a set of commonly exposedadjacent images from which a merged image or video frame may be createdas a high-resolution image and/or video frame, and which would benefitfrom color correction based on lack of color fidelity resulting fromcreation of a merged high-resolution image. Although the imaging cameraarray is illustrated as a rectangular grid, the imaging camera array maybe arranged with array cameras in various configurations. One example ofanother embodiment of an semi-spherical imaging camera array is given inMarks, D. L., H. S. Son, J. Kim, and D. J. Brady, Engineering AGigapixel Monocentric Multiscale Camera. Optical Engineering, 2012.51(8)

Reference camera 195 may comprise a lower resolution camera utilized toprovide a reference image having a high color quality reference image.For example, where the color depth of an array camera pixel may be onthe order of 8 bits or 16 bits, the color depth of the reference cameramay be on the order of 24 bits. However, the resolution of a referenceimage from the reference camera will be much lower than a merged highresolution image created from array images combined from the imagingcamera array.

Apparatus 100 also includes image processor 102. Image processor 102 mayinclude, for example, a microprocessor 110, random access memory 120,nonvolatile storage 130, a display 150, an input device 160, a signalgeneration device 190, and a network interface device 140. In certainembodiments, the image processor 102 may comprise a personal computer,mobile computer, mobile phone, tablet, or other suitable processingdevice. In other embodiments, the image processor 100 may comprise anapplication-specific integrated circuit were in the functions describedbelow are implemented in hardware.

Illustrated in non-volatile storage 130 are functional components whichmay be implemented by instructions operable to cause processor 110 toimplement one or more of the processes described below. Whileillustrated as part of non-volatile storage 130, such instructions mayoperate to cause the processor to perform various processes describedherein using any one or more of the hardware components illustrated inFIG. 1. These functional components include an image stitcher 132, aglobal color corrector 134, a localized color corrector 136 and an imagecapture controller 138. The image stitcher 132 may operate to combinecommonly exposed array images from imaging camera array 155 into asingle high resolution image. A global color corrector 134 may operateto perform a color correction process as described herein to apply colorcorrection to a high resolution image combined from the commonly exposedarray images. The localized color corrector may operate to perform acolor correction process on individual ones of commonly exposed arrayimages prior to combination of the commonly exposed array images into ahigh resolution image. The image capture controller 138 may provide asignal to the sync controller to create commonly exposed array imagesand reference images of a common or overlapping field of view of theimaging camera array and the reference camera. In another embodiment,image capture controller need not be used, and image capture control isprovided by sync controller 175.

Sync controller 175 and image processor 102 may be combined as a singledevice or as separate devices. In another embodiment, the imaging cameraarray 155 and reference camera 195 along with the sync controller 175and image processor 102 may be incorporated into a single housing as anintegrated device. Single housing embodiments can include mobileprocessing devices such as tablets and hand-held processing deviceshaving processors and cellular radios, such as cellular telephones.

Non-volatile storage 130 may comprise any combination of one or morecomputer readable media. The computer readable media may be a computerreadable storage medium. A computer readable storage medium may be, forexample, but not limited to, an electronic, magnetic, optical,electromagnetic, or semiconductor system, apparatus, or device, or anysuitable combination of the foregoing. More specific examples (anon-exhaustive list) of the computer readable storage medium wouldinclude the following: a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an appropriateoptical fiber with a repeater, a portable compact disc read-only memory(CD-ROM), an optical storage device, a magnetic storage device, or anysuitable combination of the foregoing. In the context of this document,a computer readable storage medium may be any tangible medium that cancontain, or store a program for use by or in connection with aninstruction execution system, apparatus, or device.

Where image processor 102 is a general purpose computer system, thecomputer system can include a set of instructions that can be executedto cause the image processor 102 to perform any one or more of themethods or computer based functions disclosed herein. Computer programcode for carrying out operations for aspects of the present disclosuremay be written in any combination of one or more programming languages,including an object oriented programming language conventionalprocedural programming languages. The program code may execute entirelyon the image processor 102, partly on the image processor 102, as astand-alone software package, partly on the image processor 102 andpartly on a remote computer, or entirely on the remote computer orserver. In the latter scenario, the remote computer may be connected tothe user's computer through any type of network, including a local areanetwork (LAN) or a wide area network (WAN), or the connection may bemade to an external computer (for example, through the Internet using anInternet Service Provider) or in a cloud computing environment oroffered as a service.

Aspects of the present disclosure are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatuses(systems) and computer program products according to embodiments of thedisclosure. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable instruction executionapparatus, create a mechanism for implementing the functions/actsspecified in the flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that when executed can direct a computer, otherprogrammable data processing apparatus, or other devices to function ina particular manner, such that the instructions when stored in thecomputer readable medium produce an article of manufacture includinginstructions which when executed, cause a computer to implement thefunction/act specified in the flowchart and/or block diagram block orblocks. The computer program instructions may also be loaded onto acomputer, other programmable instruction execution apparatus, or otherdevices to cause a series of operational steps to be performed on thecomputer, other programmable apparatuses or other devices to produce acomputer implemented process such that the instructions which execute onthe computer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

As illustrated in FIG. 1, the image processor 102 includes a processor110. A processor 110 for image processor 102 is configured to executesoftware instructions in order to perform functions as described in thevarious embodiments herein. A processor 110 for an image processor 102may be a general purpose processor or may be part of an applicationspecific integrated circuit (ASIC). A processor 110 for an imageprocessor 102 may also be a microprocessor, a microcomputer, a processorchip, a controller, a microcontroller, a digital signal processor (DSP),a state machine, or a programmable logic device. A processor 110 for animage processor 102 may also be a logical circuit, including aprogrammable gate array (PGA) such as a field programmable gate array(FPGA), or another type of circuit that includes discrete gate and/ortransistor logic. A processor 110 for an image processor 102 may be acentral processing unit (CPU), a graphics processing unit (GPU), orboth. Additionally, any processor described herein may include multipleprocessors, parallel processors, or both. Multiple processors may beincluded in, or coupled to, a single device or multiple devices.

Moreover, the image processor 102 includes a RAM 120 and a non-volatilestorage 130 that can communicate with each, and processor 110, other viaa bus 108. Memories described herein are tangible storage mediums thatcan store data and executable instructions, and are non-transitoryduring the time instructions are stored therein. A memory describeherein is an article of manufacture and/or machine component. Memoriesdescribed herein are computer-readable mediums from which data andexecutable instructions can be read by a computer. Memories as describedherein may be random access memory (RAM), read only memory (ROM), flashmemory, electrically programmable read only memory (EPROM), electricallyerasable programmable read-only memory (EEPROM), registers, a hard disk,a removable disk, tape, compact disk read only memory (CD-ROM), digitalversatile disk (DVD), floppy disk, blu-ray disk, or any other form ofstorage medium known in the art. Memories may be volatile ornon-volatile, secure and/or encrypted, unsecure and/or unencrypted.

As shown, the image processor 102 may further include a display unit150, such as a liquid crystal display (LCD), an organic light emittingdiode (OLED), a flat panel display, a solid state display, or a cathoderay tube (CRT). Additionally, the imaging processor may include an inputdevice 160, such as a keyboard/virtual keyboard or touch-sensitive inputscreen or speech input with speech recognition, and which may include acursor control device, such as a mouse or touch-sensitive input screenor pad.

FIG. 2 illustrates an exemplary use of the apparatus 100. As illustratedtherein, imaging camera array 155 has a field of view 215 directed at ascene 210. The field of view 215 of the imaging camera array comprisesthe combined field of views of the array cameras 155 a, 155 b, 155 c,155 d . . . 155 n. Reference camera 195 has a field of view 220 definedby the camera optics and the camera sensor where the field of view 220of the reference camera is also directed at the scene 210. When directedby the sync controller 175, imaging camera array 155 and referencecamera 195 begin imaging of scene 210. In one embodiment, synccontroller 175 controls timing of each of the imaging camera array 155and reference camera 195 such that exposures (at respective frame ratesof each of the imaging camera array 155 and reference camera 195)exposed at approximately the same time.

The output of imaging camera array 155 comprises a plurality of commonlyexposed array images of the scene 210. Commonly exposed array images maycomprise simultaneously or near-simultaneously exposed images or videoframes created by each of the array camera over time. One set ofcommonly exposed array images or frames may be used to create a highresolution image or frame. The manner of capture by the imaging cameraarray is not limited in accordance with the technology. That is, each ofthe individual array cameras can capture simultaneously, or serially, orin any sequence designed to effectively capture the scene 210.

Capture of the commonly exposed array images may be likewisesynchronized by the sync controller 175 with the capture of referenceimages from the reference camera 195. Reference images may be commonlyexposed with a set of array images, may be simultaneously exposed with aset of array images, or may precede exposure of a set of array images.In some embodiments, one reference image may be utilized with multiplesets of commonly exposed array images or frames. In such configuration,an array imaging system may have a frame rate exceeding the frame rateof the reference camera and the reference image utilized in theprocesses described below may comprise a last-in-time image createdprior to the color correction process applied to a particular set ofarray images.

Reference camera 195 has a high color fidelity and quality to capturethe color of scene 210. The resolution of reference camera 195 can besignificantly lower than the resulting stitched image generated from thearray images in the imaging camera array.

Imaging camera array 155 has an effective field of view illustrated bylines 215 which encompasses the scene 210. Reference camera 195 likewisehas a field of view represented by lines 220 at least partiallyoverlapping the field of view 215. The respective field of views shouldbe at least partially overlapping, with the field of view 220 ofreference camera 195 directed to provide the color reference image ofthe scene 210. The capture of the reference image and array images fromthe imaging camera array 155 need not occur exactly simultaneously, butshould occur within a timeframe such that the reference color imagerelative to a commonly exposed set of array images provides a suitabletemporal relationship to provide color correction.

FIG. 3 illustrates an overall process which may be performed by theimage processor 102 in order to create high-resolution still and videoimages. As discussed below, the overall process has several embodimentsand may be implemented by instructions operable to instruct a processor110 to complete the tasks as described herein. At 310, array images of ascene are captured and provided to the image processor 102. Array imagesare captured by the imaging camera array 155 and may comprise stillimages or video frames. One or more sets of commonly exposed arrayimages may be captured of a scene to generate one or more highresolution merged images, one merged image from each set of commonlyexposed array images. At 320, and before, after or simultaneously withstep 310, a high color quality reference image of the scene is capturedby the reference camera 195.

At 330, a color profile transform is applied to the array image datawhich makes up the high-resolution image created by the array images. Asdiscussed below, step 330 may take any number of different embodiments.In one embodiment, the array images are merged or stitched togetherusing any of a number of well-known stitching algorithms to create asingle high-resolution image to which color correction can then beapplied. Further details on this embodiment are discussed below withrespect to FIG. 4. In another embodiment, color profiles are pride toeach of the individual array images prior to the stitching or mergingprocess. Further details on this embodiment of step 330 are discussedbelow with respect to FIG. 7. At 340, a color corrected high-resolutionimage is provided.

Although FIG. 3 refers to color correction of an image, in oneembodiment, one reference image may be utilized for color correction onmultiple sets of commonly exposed array images. For example, where thearray images are sourced from a video stream having a given frame rate(fps), color correction can be applied from a single reference frame orreference image to a series of frames of array images. In oneembodiment, the reference camera may have a frame rate equal to theframe rate of the imaging camera array. In another embodiment, the framerate of the reference camera may be slower than that of the imagingcamera array. For example, if the frame rate of the imaging camera arrayis 60 fps, the same transform from a reference image or frame may beapplied to any number of frames of the video. In yet another embodiment,the frame rate of the reference camera may be greater than the imagingcamera array.

FIG. 4 illustrates a process performed by the image processor forapplying color correction to a high-resolution image after a commonlyexposed set of array images are stitched together to create ahigh-resolution image. FIG. 4 represents one embodiment of a method forperforming step 330 in FIG. 3. In one embodiment, the processillustrated in FIG. 4 may be performed by a global color corrector 134.At 410, a high color quality reference image is obtained. At 415, a setof commonly exposed array images are acquired by the image processor. At420, the high-resolution images are stitched together to create a singlehigh-resolution image. Image stitching may be performed by any of anumber of image stitching algorithms as represented by image stitcher132. Such algorithms include, without limitation, direct methodsemploying pixel-to-pixel matching as well as feature-based methodsutilizing keypoint detection and feature mapping. The illustration ofthe steps 410, 415, 420 425, 430 in FIG. 4 indicates that the steps maybe performed in parallel in one embodiment. In another embodiment, thesteps may be performed sequentially beginning with steps 410 and 415.The choice of ordering of the respective steps may vary depending uponthe particular application for which the technology is utilized.

Optionally, at 425 and 430, the reference image and the high-resolutionimage are partitioned into different color areas to provide the colorcorrection based on each partition individually. In one embodiment,partitioning is not required, hence steps for 425 and 430 areillustrated in dashed lines to indicate their optional nature. Inanother embodiment, partitioning of each of the respective images mayoccur based on any of a number of different steps. One examplepartitioning is image thresholding which separates regions of the imageinto at least two different partitions based on an intensity threshold.

At 435, a color correction transform is computed for applying the colorprofile of the reference image to the merged high-resolution image. Asindicated at 435, this transform may be computed on apartition-by-partition basis, or for the image as a whole. Examples ofthe transform computation process 435 are illustrated in FIGS. 5 and 6.At 440, the transform is applied to the image or per partition to outputa color corrected high-resolution image.

FIG. 5 illustrates one alternative embodiment for performing step 435 ofFIG. 4. FIG. 5 illustrates a process creating a color transform for amerged high resolution image based on color histogram specification.Histogram specification is performed by applying the histogram for eachcolor channel per image or per partition from the reference image to themerged high-resolution image. At step 510, a histogram P_(d)(w) for thereference image (or partition) is created. The cumulative distributionfunction for the reference image (or partition) is created at 530 and isdescribed by:

T(d)=∫₀ ^(d) P _(d)(w)dw

At step 520, a histogram P_(s)(w) for the target image is created. Thecumulative distribution function for the target image (or partition) maybe created at 540 and is described by:

G(s)=∫₀ ^(s) P _(s)(w)dw

At 550, the transform calculated at 550. The transform is representedby: d=T⁻¹[G(s)].

Using the transform calculated at 550, the color profile of the targetimage is corrected by applying the transform calculated for each imageor each partition to the high resolution image or partition.

FIG. 6 illustrates another alternative for performing step 435 of FIG. 4using a color transfer process in accordance with techniques describedin Erik Reinhard et al., Color Transfer between Images, IEEE ComputerGraphics and Applications, v. 21 n. 5, p. 34-41, September 2001(hereinafter “Reinhard et al. 2001”).

At 610 and 620, each image or each image partition is transformed to lαβcolor space coordinates. This is performed by first converting the RGBvalues of each image to a device-independent XYZ space using a firsttransformation matrix and then to LMS space using a secondtransformation matrix, followed by converting the data to logarithmicspace where L=log L, M=Log M and S=Log S. This conversation from RGB tolαβ color space allows the l axis to represent an achromatic channel,and the α and β channels to represent chromatic yellow-blue andred-green component channels, respectively.

At 630 and 640, the mean and variance of each image is created. The meanand standard deviations provide a set of points in lαβ space to transferbetween the respective images or partitions. The mean and standarddeviation are calculated separately for each axis in lαβ space. Firstthe mean is subtracted from each of the lαβ space data points:

l*=l−

l

α*=α−

α

β*=β−

β

Next, the data points are scaled by factors determined by theirrespective standard deviations:

$l^{\prime} = {\frac{\sigma_{t}^{l}}{\sigma_{s}^{l}}l^{*}}$$\alpha^{\prime} = {\frac{\sigma_{t}^{\alpha}}{\sigma_{s}^{\alpha}}\alpha^{*}}$$\beta^{\prime} = {\frac{\sigma_{t}^{\beta}}{\sigma_{s}^{\beta}}\beta^{*}}$

After this transformation, the resulting data points have standarddeviations that conform to the photograph. Next, instead of adding theaverages that we previously subtracted, we add the averages computed forthe photograph.

At 650 the data points derived from the reference image are applied toeach merged image or each merged image partition. At 660, the image isconverted back to the RGB color space for display.

FIG. 7 illustrates another embodiment for applying color correction tohigh resolution imaging created from a plurality of array images usingapparatus 100. The process of FIG. 7 may be referred to herein aslocalized color correction in that color correction is applied to eachof the plurality of array images prior to creating a merged highresolution image. In another embodiment, an edge color correctionprocess may also be applied prior to merging the array images into ahigh resolution image. The process of FIG. 7 may be performed by alocalized color corrector 136, in FIG. 1. FIG. 7 represents anotherembodiment of a method for performing step 330 in FIG. 3.

At 710 and 715, a reference image and a plurality of array images areobtained, respectively. Obtaining the images at 710 and 715 isequivalent to steps 410 and 415 in FIG. 4. One reference image may beused for each commonly exposed set of array images or for multiple setsof array images, depending on the frame capture rate of the respectivereference camera 195 and imaging camera array 155.

Steps 720, 730, 740 and 750 are applied for each array image in the setof commonly exposed array images obtained at 715.

At 720, for each array image (i), a matching area between the referenceimage and each array image is determined by, for example, detectingfeature points in the array image (i) at 722 and matching the featurepoints determined in 722 to the reference image at 724. In oneembodiment, a scale invariant feature detector such as the scaleinvariant feature transform (SIFT) (Lowe, David G. (1999). “Objectrecognition from local scale-invariant features”. Proceedings of theInternational Conference on Computer Vision 2. pp.1150-1157.doi:10.1109/ICCV.1999.790410) may be used. Generally,keypoints of objects in image (i) are determined at 722 and acorresponding feature points (or objects) are matched in the referenceimage at 724 by comparing each feature from image (i) to the referenceimage to find matching features based on Euclidean distance of theirfeature vectors.

At 730, a matching area transform is computed to apply the featurepoints to the reference image. The transform comprises a transformationmatrix comprising a generally planar homography matrix applies therespective determined feature points to matching feature points in thereference image. Since each array image is only a portion of the fieldof view of the reference camera (and hence the reference image), thetransformation matrix is utilized to determine a cropping area of thereference image matching the array image.

At 740, the image is cropped by first calculating a window for thereference image and then cropping the reference image using thecalculated window. At 742, this cropping is performed by determining acropping window using the transformation matrix in the reference image,following at 744 by cropping the reference image using the calculatedcropping window from 742. The color profile of the cropped referenceimage will be used apply color correction to each array image.

At 750, the color profile of the cropped portion of the reference imageis applied to the array image (i) to output a color corrected arraymimage (i). At 760, if additional array images (i+1) exist, then the loopcontinues until all images in the commonly exposed set of array imagesare color corrected.

When all images (i_(n)) in the commonly exposed set of array images havebeen corrected, the array images are joined at 780 to create a colorcorrected high resolution image comprising a merged image of thecommonly exposed set of array images.

Optionally at 770, edge color correction may be applied to images tocorrect for variances in overlapping areas of adjacent array images. Theedge correction process may be optional and is discussed below withrespect to FIG. 10.

At 780, the color-corrected array images are stitched to create ahigh-definition array image.

FIGS. 8 and 9 present two embodiments of the application of the colorprofile of the reference image crop to the array image. In theembodiment illustrated in FIG. 8, a histogram specification process isperformed to transfer the color in the cropped referent image to theindividual array image. In FIG. 9, a color transfer process inaccordance with techniques described in Reinhard et al. 2001. lαβcorrection as discussed above with respect to FIG. 6 is used.

FIG. 8 illustrates the steps of FIG. 7 in that for each array image (i)in a commonly exposed set of array images at 810, steps 720, 730 and 740are performed as discussed above with respect to FIG. 7. In theembodiment of FIG. 8, step 750 in FIG. 7 may be performed by a histogramspecification process similar to that described above with respect toFIG. 5.

In this embodiment, the histogram specification process is appliedbetween the cropper portion of the reference image and each array imagein a commonly exposed set of array images. As such, a color histogramfor the source (reference crop) image is determined at 835 followed by adetermination of a color histogram for the target (i th array image) at840. At 845, a transform of the form is determined. At 850, thetransform for the cropped reference image to the ith array image toprovide a color corrected array image (i). The process proceeds at 760to the next (i+1) image until all images (frames) from the image arrayare processed.

At 860, the for loop which began at 810 of the method of FIG. 8 iscomplete, and the loop returns to step 810 until all array images areprocessed.

FIG. 9 likewise illustrates the steps 720, 730 and 740 of FIG. 7 thatare performed for each array image (i) in a commonly exposed set ofarray images at 810. In the embodiment of FIG. 8, step 750 in FIG. 7 maybe performed by a color transfer process in accordance with Reinhard etal. 2001. At 935, each image is transformed to the lαβ coordinate space.At 940, the mean and variance of each of the array image and the croppedreference image portion are determined, and at 945, the color profile ofthe reference image portion is applied to the array image. The processproceeds at 760 to the next (i+1) image until all images (frames) fromthe image array are processed.

At 955, the array images are returned to the RGB color space fordisplay. Note that step 955 may be performed before or after thestitching process.

At 960, the for loop which began at 910 of the method of FIG. 9 iscomplete, and the method returns to step 910 until all array images areprocessed.

In the localized embodiment, issues may occur in the application ofreference color profiles to individual array images resulting inoverlapping regions of adjacent images having mis-matched or slightlydifferent color profiles. Hence, in one embodiment of FIG. 7, an edgecorrection process may be performed for those array images having anoverlapping adjacent array images.

FIG. 10 illustrates the color correction process for overlapping imagepairs, also referred to herein as edge correction. The processillustrated in FIG. 10 is a pair-wise process in that correction isperformed for each pair of overlapping images such that the colordifferences between two overlapping regions in array images fromadjacent array cameras are minimized.

Initially, at 1010, a global cost function is created for the overallcorrection process based on a robust error function. The global costfunction accounts for each image i, each pixel j belonging to the set ofpixels overlapping with the ith image, and all pixel matching pairs k inthe overlapping regions between the overlapping images.

The global cost function is minimized to reduce the potential effect ofoutlier pixel pair matching errors in the color correction valuescreated in the edge error correction process. At 1010 global costfunction may be used to describe the correction process (Equation 1) as:

e=Σ _(i=1) ^(n)Σ_(jεl(i))Σ_(kεM(i,j)) f(r _(i j) ^(k))²

Where:

l(l) denotes the images overlapping with the ith image;

M(i,j) is the set of pixel matching pairs in the overlapping regionsbetween the overlapping images; and

r_(i j) ^(k) is the error function for each pixel matching pair.

The error function r_(i j) ^(k) has the following form (Equation 2):

$r_{ij}^{k} = {B_{ij}^{k_{i}} - {g( {{g^{- 1}( B_{ij}^{k_{i}} )}\frac{c_{j}}{c_{i}}} )}}$

where g is the camera response function;

$B\frac{k_{i}}{ij}$

is the color value of one channel of the source pixel in the pixelmatching pair; and

$B\frac{k_{j}}{ij}$

is the color values of the destination pixel in the pixel matching pair;and

C_(i) is the color gain value for one channel of the ith image; and

C_(j) is the color gain value for one channel of the jth image.

i is an index of all images in a set of commonly exposed array images. jis an index of all images overlapping with any ith image. k is the indexof overlapping region pixels.

The error function e defined the total error of all the overlappingregions of all the picture pairs in a set of array images and minimizingthe global error function allows one to solve for the color gain valuesC_(i) for each image i. Multiplying each color gain value per channelwith the image provides a corrected color in the overlapping (or edge)regions of the ith image. After stitching, the images are warped to aposition in the final stitching coordinates, allowing determination ofthe overlapping region and the pixel matching pairs.

An assumption implicit in the foregoing equation 2 is that twooverlapping pixels, one each in adjacent array images, should have thesame color value. However, due to variations in the camera perspective,camera sensors, exposure, and possibly other factors, in reality thismay not be the case. An ideal solution for the error function wouldresult in zero—no error—which would result in a simple solution forC_(i). Because most cases are not ideal, the robust error functionremoves outlier matches from having too great an impact on thecorrection calculation.

Because there is a potential for error from incorrect or outlier pixelmatching pairs, a robust error function is used to limit the effect ofsuch outlier errors:

${f(x)} = \{ \begin{matrix}{{x},} & {{{if}\mspace{14mu} {x}} < x_{{ma}\; x}} \\{x_{{ma}\; x},} & {{{if}\mspace{14mu} {x}} \geq x_{{ma}\; x}}\end{matrix} $

Once the global cost function is completed, for each array image (i)having an overlapping image, pixel matching pairs are obtained using theimage stitching process. After image stitching, the images are warpedinto a position in the final stitching coordinate, therefore theoverlapping region can be determined by matching the pixels.

Each color channel will have a color gain value such that the process ofFIG. 10 is performed on a per color channel basis. Equation 1 isminimized with respect to all the color value gains for one colorchannel by non-linear optimization methods, such as Levenberg-Marquardtmethod.

Using this methodology, at 1020 for each image i having an overlappingimage j, at 1030, pixel matching pairs in overlapping regions betweenthe overlapping image regions of the respective images i, j aredetermined using the pixel matching component of the stitching processultimately used to create the merged high resolution image. At 1040, foreach image i, and for each overlapping image j (1050) and for all pixelsin the overlapping images (1060), the color gain value for each RGBchannel between the pair of pixels is determined at 1070. The loopcontinues at 1075 until all color gain values for all images aredetermined. At 1080, the global cost function is minimized using, forexample, a Levenberg-Marquardt with respect to C_(i) to obtain a colorgain value for each of the plurality of array images i. The color gainvalue C_(i) obtained is thus an optimal color gain value given theconstraints of processing a high resolution set of array images. At 1090the color gain values for each image are applied to the images prior tostitching. After color this edge correction, there may be still somelocal color mismatches between adjacent images. Such color mismatchescan be hidden by the seam finding process and blending process in thestitching algorithm, which is performed after color correction at step780 in FIG. 7.

The technology advantageously provides high resolution color imagingfrom an imaging camera array using relatively standard array hardwarewith more accurate representation of the field of view being imaged. Thecolor correction provided by the present technology has the advantage ofbeing more technically accurate than prior techniques used on highresolution images as such prior techniques were not based on high colordepth reference images. The system allows for high definition imaging ofvarious scenes using generally available technology while improving onthe ability of such technology to provide color-accurate, highresolution imaging. Errors which may arise by applying standard or knowncolor correction techniques are minimized or removed using theprocessing technology described herein. In addition, the technologyadvantageously provides various color correction techniques based on theapplication of the reference image color before creating a highresolution image or after creating the high resolution image, allowingone to tailor the color correction techniques based on the applicationfor which the technology is applied.

In accordance with the above advantages, a means for capturing aplurality of sets of commonly exposed images of a scene, each setsuitable for creating a high resolution image or video frame, isprovided. The means may comprise an imaging camera array 155. A meansfor capturing a reference image which has a color depth exceeding themeans for capturing the plurality of sets is also provided. The meansfor capturing a reference image may comprise a reference camera 195. Ameans for synchronizing the means for capturing to create commonlyexposed sets of images and reference images is also provided. A meansfor applying a color correction to the sets of commonly exposed imagesbased on the reference image to create a color-corrected high resolutionimage is also provided. The means for applying a color correction mayinclude an image processor 102. The means for applying a colorcorrection may include means for applying a color correction to each setof commonly exposed images prior to creating a high resolution image orvideo frame, and/or means for applying a color correction to a highresolution image or video frame after creation of such frame from a setof commonly exposed images. The means for applying a color correctionmay include means for applying a overlapping area color correction tooverlapping ones of the plurality of commonly exposed images in a set ofcommonly exposed images.

In the aforementioned description, the figures present variousembodiments of processing using a reference image and an array image. Inembodiments where processes are performed on ones of array images of acommonly exposed set of array images, parallel processing of any numberof array images from a set may occur in relation to a reference image inorder to increase processing speed.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

What is claimed is:
 1. An imaging apparatus, comprising: a camera arraycomprising a plurality of imaging cameras each having a camera field ofview, each camera field of view at least partially overlapping withrespect to at least one adjacent imaging camera field of view to providean array field of view; a reference camera having a field of view atleast partially overlapping the array field of view; a synchronizationcontroller coupled to the camera array and the reference camera, thesynchronization controller adapted to direct the reference camera andplurality of imaging cameras to capture a scene, the reference cameraadapted to provide at least one reference image of the reference camerafield of view and the plurality of imaging cameras adapted to provide aplurality of array images of the array field of view; and an imageprocessor adapted to apply a color correction based on the at least onereference image to a high resolution image formed from the plurality ofarray images.
 2. The imaging apparatus of claim 1 wherein the cameraarray and the reference camera commonly capture the scene at the sametime.
 3. The imaging apparatus of claim 1 wherein the imaging cameraarray is adapted to capture video imaging having a frame rate and thereference camera is adapted to capture images at a frame rate less thanthe frame rate of the imaging camera array, the image processor adaptedto apply the color correction based on the at least one reference imageto multiple high resolution images formed from multiple sets of arrayimages.
 4. The imaging apparatus of claim 1 wherein a set of arrayimages is commonly exposed and the image processor is adapted to applythe color correction to each of array image in the set of array imagesand thereafter merge the set of array images into the high resolutionimage.
 5. The imaging apparatus of claim 4 wherein the image processoris operable to apply an edge color correction to each image in the setof array images prior to the merge of the set of array images.
 6. Theimaging apparatus of claim 1 wherein the high resolution image is amerged image of a plurality of commonly exposed array images, and theimage processor is operable to apply the color correction based on thereference image to the merged image.
 7. A method of creating a colorcorrected high resolution image, comprising: obtaining a set of aplurality of at least partially overlapping commonly exposed arrayimages of a first field of view of a scene using a camera arraycomprising a plurality of imaging cameras; obtaining a reference imageof a second field of view including the scene using a reference camera,the reference image having a color depth greater than each of theplurality of at least partially overlapping commonly exposed images, thefirst field of view and second field of view at least partiallyoverlapping; and applying a color correction to the plurality of atleast partially overlapping images based on the color depth of thereference image to create a color-corrected high resolution image usingan image processor.
 8. The method of claim 7 wherein applying a colorcorrection comprises merging the plurality of partially overlappingcommonly exposed array images using a stitching process to create a highresolution color image followed by applying the color correction to thehigh resolution color image.
 9. The method of claim 7 wherein applying acolor correction comprises applying the color correction to each of theplurality of partially overlapping commonly exposed array imagesfollowed by creating a high resolution merged image by applying astitching process to the plurality of partially overlapping commonlyexposed array images.
 10. The method of claim 7 wherein applying a colorcorrection comprises: applying a color transform from the referenceimage to each of the plurality of partially overlapping commonly exposedarray images; determining overlap regions between adjacent ones of eachof the commonly exposed images; determining corresponding pixel pairs ineach of the overlap regions; calculating a color gain value between eachof the adjacent ones of the commonly exposed images based on thecorresponding pixel pairs in the overlap regions; and applying the colorgain value to each of the adjacent ones of the commonly exposed images.11. The method of claim 10 wherein the calculating a color gain valuecomprises solving for a color gain value (Ci) for each image pair usingan error function based on a camera response, the color gain value of apixel in a pixel pair from one image in the pixel pair a color gainvalue of a matching pixel in another image in the pixel pair.
 12. Themethod of claim 11 wherein the method further includes calculating thecolor gain value for each color channel of each image having overlappingimages and for each pixel pair, and minimizing a global error todetermine an optimal color gain value for each image, wherein applyingthe color gain value comprises applying the optimal color gain value foreach image.
 13. The method of claim 11 wherein the method furtherincludes obtaining multiple sets of a plurality of at least partiallyoverlapping commonly exposed images of a field of view of a first scene,each set comprising one of a plurality of frames captured at a framerate, and wherein applying a color correction comprises applying thecolor correction to each of the sets.
 14. The method of claim 11 whereinobtaining a reference image comprises obtaining multiple referenceimages at a frame rate less than or equal to the frame rate at which thesets of the plurality of overlapping commonly exposed images arecaptured, and wherein applying a color correction comprises applying acolor correction base on the reference image captured nearest in timeprior to a time at which a set of overlapping commonly exposed imagesare captured.
 15. An high resolution imaging device comprising: a firstcamera system adapted to generate video imaging comprising a pluralityof frames, each frame comprising a set of commonly exposed images of ascene, each of the images in the set of commonly exposed imagesincluding at least a portion of a field of view of the scene and atleast partially overlapping at least one adjacent image having adifferent portion of the field of view; a second camera system adaptedto generate a plurality of reference images of the scene from areference field of view, each of the plurality of reference imageshaving a color depth greater than a color depth of each of the pluralityof commonly exposed images, at least a portion of the plurality ofreference images being commonly exposed with ones of the plurality offrames; an image processor including a color corrector operable to applya color correction based on at least one of the plurality of referenceimages to a corresponding one of the plurality of frames, the colorcorrection applied to each of the set of commonly exposed images of thescene relative to a matched portion of the at least one of the pluralityreference images to provide a set of color-corrected plurality images;and an image stitcher operable to create a high resolution image fromthe color corrected plurality of images.
 16. The high resolution imagingdevice of claim 15 further including a synchronization controllercoupled to the first camera system and the second camera system, thesynchronization controller operable to instruct the first camera systemand the second camera system to create the video imaging and thereference images of the scene.
 17. The high resolution imaging device ofclaim 15 wherein the color corrector includes instructions operable tocalculate a color gain value (C_(i)) for each of an image paircomprising a portion of the at least one of the plurality of referenceimages and one of the commonly exposed images using an error functionbased on a camera response function, the color gain value of a pixel ina pixel pair from the portion of the at least one of the plurality ofreference images, and a color gain value of a matching pixel in said oneof the commonly exposed images in the pixel pair.
 18. The highresolution imaging device of claim 17 wherein the color correctionfurther includes calculating the color gain value for each color channelof each image in the commonly exposed images having overlapping otherones of the commonly exposed images and for each pixel pair inoverlapping areas of the images, and minimizing a global error todetermine an optimal color gain value for each image.
 19. The highresolution imaging device of claim 18 wherein the color correctionfurther includes applying the optimal color gain value to each image inthe set of commonly exposed images.
 20. The high resolution imagingdevice of claim 19 further including creating a high resolution framefrom the set of commonly exposed images.